(Bloomberg) — The head of the World Bank compared cryptocurrencies to “Ponzi schemes,” the latest financial voice to raise questions about the legitimacy of digital currencies such as Bitcoin.

“In terms of using Bitcoin or some of the cryptocurrencies, we are also looking at it, but I’m told the vast majority of cryptocurrencies are basically Ponzi schemes,” World Bank Group President Jim Yong Kim said Wednesday at an event in Washington. “It’s still not really clear how it’s going to work.”

Jim Yong Kim speaks during a Bloomberg Television interview at the International Monetary Fund (IMF) and World Bank Group Annual Meetings in Washington, D.C. Photographer: Andrew Harrer/Bloomberg

The development lender is “looking really carefully” at blockchain technology, a platform that uses so-called distributed ledgers to allow digital assets to be traded securely. There’s hope the technology could be used in developing countries to “follow the money more effectively” and reduce corruption, Kim said.